Phosphorous passivation of the SiO2/4H–SiC interface

We describe experimental and theoretical studies to determine the effects of phosphorous as a passivating agent for the SiO₂/4H–SiC interface. Annealing in a P₂O₅ ambient converts the SiO₂ layer to PSG (phosphosilicate glass) which is known to be a polar material. Higher mobility (approximately twice the value of 30–40 cm²/V s obtained using nitrogen introduced with an anneal in nitric oxide) and lower threshold voltage are compatible with a lower interface defect density. Trap density, current–voltage and bias-temperature stress (BTS) measurements for MOS capacitors are also discussed. The BTS measurements point to the possibility of an unstable MOSFET threshold voltage caused by PSG polarization charge at the O–S interface. Theoretical considerations suggest that threefold carbon atoms at the interface can be passivated by phosphorous which leads to a lower interface trap density and a higher effective mobility for electrons in the channel. The roles of phosphorous in the passivation of correlated carbon dangling bonds, for SiC counter-doping, for interface band-tail state suppression, for Na-like impurity band formation and for substrate trap passivation are also discussed briefly.     

Comparison of 3C–SiC, 6H–SiC and 4H–SiC MESFETs performances

A comparative analysis of the main DC and microwave performances of MESFETs made of the commercially available silicon carbide polytypes 3C–SiC, 6H–SiC and 4H–SiC is presented. In this purpose, we have developed an analytical model that takes into account the basic material properties such as field dependent mobility, critical electric field, ionization grade of impurities, and saturation of the charge carrier velocity. For a better precision in appreciating device characteristics in the case of a short gate device, the influences of the gate length and parasitic elements of the structure, e.g. source and drain resistances, are considered too. Cut-off frequency f_T, the corresponding output power P_m and the thermal stability are also evaluated and compared with the available experimental data, revealing the specific electrical performances of MESFETs, when any of the three polytypes is used in device fabrication.     

迈拓4D040H2硬盘

硬盘,对于使用电脑的用户来说是一种非常主要的信息、数据存储工具,同时也是决定电脑性能好坏的重要部件。硬盘工作的稳定性能和数据传输速度是衡量硬盘的重要指标,同时,硬盘的容量大小也是消费者关注的问题,当然到底多大的硬盘容量最合适,还是要根据不同用户的需求来定。     

迈拓4D040H2硬盘

键盘是电脑的一种重要的信息输入设备,一款好的键盘操作起来快捷、舒适,完全可以提高使用者的信息输入效率。这是两款由旭丽电子有限公司推出的键盘,型号分别为SK-720和SK-1688。这两款键盘都采用     

4H–SiC BJTs with current gain of 110

4H–SiC BJTs with a common emitter current gain of 110 have been demonstrated. The high current gain was attributed to a thin base of 0.25 μm which reduces the carrier recombination in the base region. The device open base breakdown voltage (BV_CEO) of 270 V was much less than the open emitter breakdown voltage (BV_CBO) of 1560 V due to the emitter leakage current multiplication from the high current gain by “transistor action” of BJTs. The device has shown minimal gain degradation after electrical stress at high current density of >200 A/cm²up to 25 h.     

Physicochemical Interactions in the GeSb2Te4–PbSb2Te4 System

Semiconductors - For the first time, the GeSb2Te4–PbSb2Te4 section of the GeTe–Sb2Te3–PbTe quasi-ternary system is investigated by complex methods of physicochemical analysis...     

北京机场奥运期间C2H4变化特性

大气中的挥发性有机物是空气中影响人体健康的重要污染物,它们在光化学烟雾、酸雨、全球变暖等环境问题中也起到重要作用.使用傅里叶变换红外光谱测量了奥运期间首都机场C2H4浓度变化,通过最小二乘法拟合得到C2H4在不同时间段内的浓度值.C2H4/C2H6值的变化趋势是晚上较高,白天较低,受汽车尾气影响.C2H4浓度变化则是受机动车和飞机尾气的共同影响.奥运会期间C2H4浓度变化受飞机影响很大,浓度变化和飞机架次相关性很好.     

Regulating the Metallic Cu–Ga Bond by S Vacancy for Improved Photocatalytic CO2 Reduction to C2H4

Artificial photosynthesis, which converts carbon dioxide into hydrocarbon fuels, is a promising strategy to overcome both global warming and energy crisis. Herein, the geometric position of Cu and Ga on ultra-thin CuGaS₂/Ga₂S₃ is oriented via a sulfur defect engineering, and the unprecedented C₂H₄ yield selectivity is ≈93.87% and yield is ≈335.67 µmol g⁻¹ h⁻¹. A highly delocalized electron distribution intensity induced by S vacancy indicates that Cu and Ga adjacent to S vacancy form Cu–Ga metallic bond, which accelerates the photocatalytic reduction of CO₂ to C₂H₄. The stability of the crucial intermediates (*CHOHCO) is attributed to the upshift of the d-band center of ultra-thin CGS/GS. The C–C coupling barrier is intrinsically reduced by the dominant exposed Cu atoms on the 2D ultra-thin CuGaS₂/Ga₂S₃ in the process of photocatalytic CO₂ reduction, which captures *CO molecules effectively. This study proposes a new strategy to design photocatalyst through defect engineering to adjust the selectivity of photocatalytic CO₂ reduction.     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

C2H2／H2／SiH4等离子体聚合及其沉积物的结构与性能的研究

利用Ｃ２Ｈ２／Ｈ２／ＳｉＨ４混合单体等离子体聚合沉积在ＨＤＰＥ板表面制备薄膜，发现薄膜与ＨＤＰＥ粘接良好，Ｈ２使薄膜与基体附着性能提高但其沉积速率下降，而引入ＳｉＨ４则使薄膜的耐磨性能有较大的提高。ＩＲ和ＸＰＳ光谱表明：薄膜中含有较多的－ＯＨ，Ｏ－Ｃ，Ｃ－Ｓｉ和Ｓｉ－Ｏ基团，随着ＳｉＨ４／Ｈ２的增加薄膜中的Ｃ／Ｓｉ比可达１．２２２，说明产物的结构介于无机材料和有机物之间。     

MPEG-4第2部分与H.264比较

MPEG-4第2部分和H.264是最新的视频编码标准，分析和比较这两种视频编码标准，在此基础上对设计视频编码标准提出一些看法。     

海尔H2

滑动式操作、手机电视功能 有着与iPhone相近外形的海尔全新触摸屏手机H2显然更加时尚。除了传统黑色外,H2还拥有白色、红色以及粉色款式。3英寸的镜面屏幕拥有400×240像素分辨率,支持滑动式操作,无论是主菜单、电话簿还是音乐或彩信,掌控都更加得心应手。H2拥有221MHz处理器,背部设计有200万像素摄像头,在娱乐功能方面,还拥有手机电视等功能。同时在安全性上,H2提供了安全钥匙、防火墙、信鸽防丢以及T卡备份等功能,令使用更加安心。     

Carrier lifetime investigation in 4H–SiC grown by CVD and sublimation epitaxy

Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 μs may be observed in the mid-region of 40 μm thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the ‘true’ lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.     

Sol–gel-synthesized mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystals and their photocatalytic sensitized H2 production activity under visible light irradiation

The purpose of this work was to investigate, in the first study of its kind, hydrogen production by photocatalytic water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled TiO₂–ZrO₂ mixed oxide nanocrystal photocatalysts. The mesoporous-assembled TiO₂–ZrO₂ mixed oxide nanocrystals, with various TiO₂-to-ZrO₂ molar ratios, were synthesized by a sol–gel method with the aid of a structure-directing surfactant. The synthesized nanocrystals were characterized by thermogravimetric and derivative thermogravimetric analyzer, N₂ adsorption–desorption, X-ray diffraction, UV–visible spectroscopy, scanning electron microscope–energy-dispersive X-ray analyzer, and transmission electron microscope analyses. Parameters affecting the photocatalytic activity, including calcination conditions and phase composition, were mainly discussed. Experimental results showed that the incorporation of ZrO₂ with suitable contents could preserve the mesoporous-assembled structure of TiO₂ at high calcination temperatures and enhance its thermal stability significantly. Results of the photocatalytic-sensitized hydrogen production revealed that the TiO₂–ZrO₂ mixed oxide photocatalyst, with a TiO₂-to-ZrO₂ molar ratio of 95:5, calcined at 800 °C for 4 h, provided maximum photocatalytic hydrogen production activity. The optimized TiO₂–ZrO₂ mixed oxide photocatalyst can be considered as a potential photocatalyst for hydrogen production under solar light irradiation.     

Band structure anisotropy effects on the hole transport transient in 4H–SiC

We study the role of band structure anisotropy on the hole transport in 4H–SiC during the transient regime. For the same strength of the applied electric field, the drift velocity overshoot of the hole is stronger and reaches steady state later when the field is applied perpendicular to the c-axis, than when the field is in the c-axis direction. In both cases, the time for the hole drift velocity and mean energy to reach steady state is under 50 fs, depending on the electric field strength, and are one order of magnitude shorter than the time for the electron drift velocity and mean energy to attain the steady state.     

Halogen adsorption at an As-stabilized β2–GaAs (001)–(2 × 4) surface

Halogen (F, Cl, Br, and I) adsorption at an As-stabilized GaAs (001) surface with the β2–(2 × 4) reconstruction is studied using the plane-wave projected-augmented wave method. The effect of halogens on the structural and electronic characteristics of the semiconductor surface is analyzed. The T₂′ site at the missing row edge is shown to be the energetically most favorable for the adsorption of F, Cl, and Br, whereas I prefers the H₃ site between adjacent arsenic dimers in the third layer from the surface. Ga-halogen bond formation suggests that charge is transferred via the depletion of occupied orbitals of the As-dimer surface atoms, which leads to the weakening of Ga–As bonds in the substrate. The weakening of bonds between substrate-surface atoms due to the interaction of halogens with the surface is estimated.     

反应条件对液相沉淀法制备FePO4·2H2O的影响

以FeSO4·7H2O,NH4H2PO4,H2O2和NH3·H2O为原料,通过液相沉淀法制备得到FePO4·2H2O,研究了反应温度、搅拌速度、H2O2加入量和pH值等反应条件对合成FePO4·2H2O的影响.采用TG-DTA,XRD和SEM及ICP等测试方法对FePO4·2H2O的物相、结构及形貌进行表征.结果表明:...     

C2H4,NH3及C3H6的脉冲激光光声谱

本文用光声法检测了9.2～10.8μm波长范围内C_2H_4、NH_3及C_3H_6分子对CO_2激光的吸收特性,获得了这三种气体分子的单脉冲激光光声光谱,测量了光声信号随实验参量(样品气压、激光能量)的变化关系,用光声法获得了样品气体中的声速及各种气体分子的V-T驰豫时间。